The disclosure of Japanese Patent Application No. 2002-163578 filed on Apr. 26, 2002, including the specification, drawings and abstract is incorporated herein by reference in its entirety.
1. Field of the Invention
This invention relates to a fuel injection timing control apparatus for an in-cylinder injection internal combustion engine, which controls a fuel injection in an in-cylinder injection internal combustion engine in which fuel is directly injected into a cylinder.
2. Description of the Related Art
In the past, an in-cylinder injection internal combustion engine in which fuel is directly injected into a cylinder of the internal combustion engine has been proposed. This in-cylinder injection internal combustion engine aims to improve fuel economy and the like by precisely controlling the mixture state of a mixture within the cylinder by injecting fuel late in the compression stroke. In this in-cylinder injection internal combustion engine, however, the following problems may occur, particularly when the engine is cold, when the fuel is directly injected into the cylinder.
That is, when the engine is cold, fuel within the cylinder does not readily atomize, resulting in a tendency for a large amount of the injected fuel to adhere to the top face of an engine piston (hereinafter referred to simply as xe2x80x9cpiston top facexe2x80x9d) and the cylinder inner peripheral face. Therefore, ordinarily when the engine is cold, the fuel injection timing is set to during the intake stroke (hereinafter referred to as xe2x80x9cintake stroke injectionxe2x80x9d), thus increasing the time between fuel injection and ignition to as long as possible to promote atomization of the injected fuel. Even if this intake stroke injection is performed, however, it is still difficult to completely prevent the adherence of fuel on the piston top face and cylinder inner peripheral face; some of the injected fuel is not burned, but remains adhered after engine combustion.
The fuel adhered to the piston top face, in particular, atomizes gradually during later engine combustion, and is discharged from the cylinder without being completely combusted, leading to a deterioration of exhaust gas emissions, such as the generation of black smoke and an increase in unburned components.
The fuel adhered to the cylinder inner peripheral face mixes with lubricating oil adhered to the cylinder inner peripheral face in order to provide lubrication for the piston. As a result, the lubricating oil is diluted by the fuel and so-called fuel dilution occurs. The lubricating oil in the cylinder that has been diluted by the fuel is scraped down the cylinder inner peripheral face from the reciprocating motion of the piston and returned to the oil pan, after which it is again supplied to the internal combustion engine to provide lubrication. Therefore, if fuel dilution of the lubricating oil occurs frequently, the ratio of fuel mixed in with the overall lubricating oil gradually increases until finally adverse effects result, such as a decline in the lubricating performance in the internal combustion engine.
Japanese Patent Laid-Open Publication No. 2001-304026 and Japanese Patent Laid-Open Publication No. 2002-13428 disclose related art in which the fuel injection timing during the intake stroke injection is set taking into consideration the distribution of the amounts of fuel adhered to the piston top face and the cylinder inner peripheral face from the fuel injection so that only one of the amounts of the adhered fuel does not increase to an extreme in order to deal with both deterioration in exhaust gas emissions and fuel dilution.
Therefore, even if the lubricating oil is diluted by the fuel following an injection of fuel into the cylinder when the engine is cold, that fuel dilution is only temporary, and unless it occurs frequently, the ratio of fuel contained in the lubricating oil to the overall lubricating oil will not change much. Further, the fuel contained in the lubricating oil decreases by gradually evaporating over time. Therefore, despite the possibility of adverse effects described above, such as a reduction in lubricating performance, ultimately caused by fuel dilution, if fuel dilution of the overall lubricating oil is at a level where it is not progressing, the adverse effects are also in a range where they can actually be effectively ignored. That is, a certain degree of fuel dilution of the lubricating oil that occurs from the injection of fuel into the cylinder can be allowed when considering the fact that the degree of the adverse effects on the internal combustion engine that are caused by that degree of fuel dilution is negligible.
On the other hand, deterioration of the exhaust gas emissions due to fuel adhered to the piston top face is to a great extent unavoidable, and the allowable range in consideration of the degree of the adverse effects on the internal combustion engine is extremely narrow.
Therefore, although fuel dilution due to an increase in fuel adhering to the cylinder inner peripheral face is allowable to some degree, it is preferable, or realistic, when fuel dilution of the overall lubricating oil is not effectively progressing, to inhibit the deterioration of the exhaust gas emissions by changing the fuel injection timing or the like so as to reduce as far as possible the amount of fuel that adheres to the piston top face.
Although the art in the foregoing publications performs fuel injection control considering both deterioration of the exhaust gas emissions due to fuel adhering to the piston top face and fuel dilution of the lubricating oil due to fuel adhering to the cylinder inner peripheral face, there still remains room for improvement with respect to flexibly dealing with these problems according to the actual degree of adverse effects they have on the internal combustion engine.
In view of this room for improvement with the related art, it is an object of this invention to provide a fuel injection control apparatus for an in-cylinder injection internal combustion engine, which can flexibly control a fuel injection mode according to an actual degree of adverse effects on the internal combustion engine from both deterioration of exhaust gas emissions caused by fuel adhering to a piston top face and fuel dilution caused by fuel adhering to a cylinder inner peripheral face.
Hereinafter, a method for solving the foregoing problems, as well as an effect of that method, will be described. According to one aspect of the invention, a fuel injection control apparatus for an in-cylinder injection internal combustion engine, in which fuel is directly injected into a cylinder of the internal combustion engine, is provided with a dilution degree estimation portion that estimates a degree of dilution by fuel in an overall lubricating oil provided to lubricate the internal combustion engine, and a control portion that controls a fuel injection mode so as to inhibit dilution by fuel of the lubricating oil when the estimated degree of fuel dilution is larger than a predetermined value.
According to this construction, when the degree of fuel dilution of the overall lubricating oil is small, for example, it is possible to give priority to suppressing the adhesion of fuel on the piston top face in order to inhibit, to as great an extent as possible, deterioration of the exhaust gas emissions, such as the generation of black smoke, and temporarily allow a fuel injection even if that fuel injection would increase the amount of fuel adhered to the cylinder inner peripheral face and cause the fuel dilution to progress. In contrast, when the degree of fuel dilution of the overall lubricating oil increases to the point where, if it progresses any farther the resultant adverse effects, such as a decline in lubricating performance, can no longer be ignored, the fuel injection mode is controlled so as to inhibit dilution by fuel of the lubricating oil. As a result, it is possible to inhibit adverse effects from the fuel dilution of the lubricating oil on the internal combustion engine.
Therefore, the fuel injection mode can be flexibly controlled according to the actual degree of adverse effects on the internal combustion engine from both the deterioration of the exhaust gas emissions caused by fuel adhesion on the piston top face and fuel dilution caused by fuel adhesion to the cylinder inner peripheral face. Accordingly, it is possible to effectively inhibit deterioration of the exhaust gas emissions and fuel dilution.
As a specific example when controlling the fuel injection mode so as to inhibit dilution by fuel of the lubricating oil in this way, the control portion of the fuel injection control apparatus for an in-cylinder injection internal combustion engine may change the fuel injection timing as the fuel injection mode so as to inhibit fuel dilution.
There is a correlation between the amount of fuel adhered to the piston top face and the piston position when the fuel is injected, as well as between the amount of fuel adhered to the cylinder inner peripheral face and the piston position when the fuel is injected, in which those amounts tend to change greatly depending on the position of the piston.
That is, as the piston moves toward top dead center when the fuel is injected, the area of the cylinder inner peripheral face covered by the piston increases, while the distance between the piston top face and the nozzle hole of the fuel injection valve decreases. As a result, the amount of fuel adhered to the cylinder inner peripheral face decreases, but the amount of fuel adhered to the piston top face increases.
In contrast, as the piston moves toward bottom dead center when the fuel is injected, the distance between the piston top face and the nozzle hole of the fuel injection valve increases, while the area of the cylinder inner peripheral face covered by the piston decreases. As a result, the amount of fuel adhered to the piston top face decreases, while the amount of fuel adhered to the cylinder inner peripheral face increases. Therefore, when changing the fuel injection timing so as to inhibit fuel dilution, it is generally sufficient to change the fuel injection timing so that injection occurs closer to when the piston reaches top dead center. Further, by changing this fuel injection timing it is possible to quite significantly, as well as quickly, change the ratio of the amount of fuel adhered to the piston top face to the amount of fuel adhered to the cylinder inner peripheral face.
Further, the fuel injection mode that is changed may be a fuel injection pressure, for example. Generally, if the fuel injection pressure is lowered, the rate at which the fuel is injected decreases. As a result, the amount of fuel that reaches the cylinder inner peripheral face decreases, resulting in a decrease in the amount of fuel adhered to the cylinder inner peripheral face. Accordingly, by changing the fuel injection pressure as well as the fuel injection timing, it is possible to even more significantly change the ratio of the amount of fuel adhered to the piston top face to the amount of fuel adhered to the cylinder inner peripheral face. As a result, fuel dilution of the lubricating oil can be inhibited even more effectively.
Lowering the fuel injection pressure, however, adversely effects atomization of the injected fuel. Therefore, if the fuel injection pressure is lowered excessively at times such as when the engine temperature (i.e., the cylinder internal temperature) is extremely low, such as during a cold start, there is a possibility that the overall amount of the fuel adhered to the piston top face and the cylinder inner peripheral face will actually increase instead of decrease. Accordingly, it is preferable also to monitor the engine temperature when changing the fuel injection pressure in this way, and set the amount of change of the fuel injection pressure according to that engine temperature or set a restriction on the amount of that change, for example.
Also, when performing a so-called divided injection, whereby the fuel injection is divided into a plurality of stages instead of just one, a division ratio of these fuel injection quantities may also be controlled as one of the fuel injection modes. In this case, the fuel dilution of the lubricating oil can be inhibited by changing the division ratio such that the fuel injection quantity of the fuel injection that is executed closer to when the piston reaches top dead center is relatively large, and the fuel injection quantity of the fuel injection that is executed closer to when the piston reaches bottom dead center is relatively small.
In addition, it is also possible to inhibit fuel dilution by changing the fuel injection quantity, such as by decreasing an increase amount value when increasing the fuel injection quantity, for example.
Furthermore, in the fuel injection control apparatus for an in-cylinder injection internal combustion engine, the dilution degree estimating portion may estimate the degree of fuel dilution based on an operating history of the internal combustion engine. With this construction, the degree of fuel dilution of the overall lubricating oil changes according to the operating state of the internal combustion engine.
For example, if a so-called cold short trip, in which the internal combustion engine is started when the engine temperature is low and is then stopped before the engine temperature has risen sufficiently, is repeated, the degree of fuel dilution increases greatly. On the other hand, if internal combustion the engine is operated for an extended period of time after it has finished warming up, fuel contained in the lubricating oil gradually evaporates during that time such that the degree of fuel dilution decreases. Therefore, the degree of fuel dilution of the overall lubricating oil can be estimated by referring to the operating history of the internal combustion engine.
Moreover, the dilution degree estimating portion may monitor whether the internal combustion engine was operating in a state in which the degree of fuel dilution increases, and estimate the degree of fuel dilution based on that monitored history. According to this construction, the degree of fuel dilution of the overall lubricating oil can accurately be estimated when it increases.
Here, when the engine temperature at engine startup is high, for example, the degree of fuel dilution of the overall lubricating oil does not increase because fuel does not adhere to the piston top face or the cylinder inner peripheral face in the first place. Therefore, it is possible to monitor the engine temperature at engine startup and determine that the engine was operating in a state in which the degree of fuel dilution increases when the engine temperature at engine startup is equal to, or less than, a predetermined temperature, for example.
Even if the engine temperature at engine startup is low, however, if the internal combustion engine continues to operate for an extended period of time thereafter, the cylinder internal temperature rises, thus inhibiting the adhesion of fuel to the piston top face and the cylinder inner peripheral face. Further, the lubricating oil temperature gradually rises from the combustion heat generated in the cylinder, so more fuel evaporates from the lubricating oil.
Accordingly, if the time from startup until stop of the internal combustion engine is sufficiently long, even if the degree of fuel dilution temporarily increases when the engine is initially operated, that degree of fuel dilution gradually decreases thereafter due to the fuel evaporating from the lubricating oil during operation of the engine. Then, either the increase in the degree of fuel dilution that occurred when the engine was initially operated is cancelled out by this decrease in the degree of fuel dilution, or, if the increase has been exceeded, there is no longer a need to retain the history which indicates that the internal combustion engine was operating in a state in which the degree of fuel dilution increased.
Accordingly, for example, the engine operating time from after engine startup until engine stop may be measured, and it can also be determined that the internal combustion engine was operating in a state in which the degree of fuel dilution increases, when, and the engine temperature at engine startup is equal to, or less than, a predetermined temperature and the engine operating time is equal to, or less than, a predetermined value.
Also, when the time from startup to stop of the internal combustion engine is the same, the cylinder internal temperature rises more quickly when a large quantity of fuel, as opposed to a small quantity of fuel, is supplied to engine combustion during that time. Therefore, adhesion of fuel to the piston top face and the cylinder inner peripheral face is inhibited at an earlier stage, and evaporation of the fuel from the lubricating oil due to the rise in temperature of the lubricating oil is also promoted to an even greater extent. There is a correlation between the rate of increase in both the cylinder internal temperature and the lubricating oil temperature, and the total amount of combustion heat generated within the cylinder after engine startup. Therefore, to accurately determine whether the internal combustion engine was operating in a state in which the degree of fuel dilution increases, it is considered preferable to monitor the total amount of combustion heat generated within the cylinder from engine startup until engine stop.
The dilution degree estimating portion may also estimate the total amount of combustion heat generated within the cylinder from engine startup until engine stop based on the engine operating state, and determines that the internal combustion engine was operating in a state in which the degree of fuel dilution increases when the engine temperature at engine startup is equal to, or less than, a predetermined temperature and the estimated total amount of combustion heat is equal to, or less than, a predetermined amount.
With this construction, it is possible to accurately determined that the internal combustion engine was operating in a state in which the degree of fuel dilution of the overall lubricating oil increases, and estimate when the degree of fuel dilution of the overall lubricating oil is high with even greater accuracy based on that determination. It is preferable that, for the engine temperature, the cylinder internal temperature, for example, be directly detected. Alternatively, however, the engine temperature can also be estimated based on, for example, an engine coolant temperature at engine startup, an intake air temperature, an ambient air temperature, or a combination of one or more of these.
Also, it is determined that the internal combustion engine was operating in a state in which the degree of fuel dilution increases when the engine temperature at engine startup is equal to, or less than, a predetermined temperature and the total amount of combustion heat is equal to, or less than, a predetermined amount. Alternatively, however, the predetermined amount to be compared to the total amount of combustion heat may also be variably set according to the engine temperature at engine startup. That is, even if the engine temperature at engine startup is equal to, or less than, the predetermined temperature, when that engine temperature is relatively high, the amount of increase in the degree of fuel dilution that occurs during initial engine operation is small so the total amount of combustion heat necessary to cancel out or exceed that amount of increase in the degree of fuel dilution is naturally less. Therefore, a construction in which the predetermined amount to be compared with the total amount of combustion heat is set smaller the higher the engine temperature at engine startup, is extremely effective in accurately determining whether the internal combustion engine was operating in a state in which the degree of fuel dilution increases.
In addition, it can be determined whether the total amount of combustion heat generated within the cylinder from engine startup until engine stop is equal to, or less than, a predetermined amount based on, for example, whether an intake air quantity sum value or a fuel injection quantity sum value, from engine startup until engine stop, is equal to, or less than, a predetermined value. The combustion heat generated within the cylinder from each fuel injection changes depending on not only the intake air quantity and the fuel injection quantity, but also the air-fuel ratio at the time of fuel injection and the ignition timing and the like. Therefore, in order to accurately estimate the amount of combustion heat, it is also effective to use a method such as placing emphasis on the intake air quantity and fuel injection quantity during those changes in the combustion heat according to the air-fuel ratio and ignition timing, and adding them up and the like.
Furthermore, the dilution degree estimating portion may determine whether the degree of fuel dilution is decreasing based on a temperature of the lubricating oil or a parameter that correlates with that temperature, and estimate the degree of fuel dilution based on the size of a counter value which is counted up when a history of operation of the internal combustion engine in a state in which the degree of fuel dilution increases has been generated, and which is gradually counted down when it has been determined that the degree of fuel dilution is decreasing. In addition, the control portion of the fuel injection control apparatus for an in-cylinder injection internal combustion engine may execute control according to the fuel injection mode based on the size of the counter value.
As described above, if operation of the internal combustion engine in a state in which the degree of fuel dilution increases, e.g., a cold short trip or the like, is repeated frequently, it will lead to a gradual increase in the degree of fuel dilution of the overall lubricating oil. On the other hand, if the internal combustion engine is operated for an extended period of time such that the lubricating oil temperature rises, the amount of fuel contained in the lubricating oil that evaporates also increases, resulting in a gradual decrease over time in the degree of fuel dilution of the overall lubricating oil.
Accordingly, by setting the counter value that changes according to an increase or decrease in the degree of fuel dilution, the degree of fuel dilution can be estimated with even greater accuracy based on the size of the counter value.
Furthermore, the dilution degree estimating portion may estimate the degree of fuel dilution by first calculating a rate of increase in the degree of fuel dilution based on a parameter that correlates with the amount of fuel adhering to the cylinder inner peripheral face from the fuel injection, then sequentially updating the degree of fuel dilution based on the calculated rate of increase and learning this updated degree of fuel dilution.
The degree of fuel dilution of the overall lubricating oil gradually progresses when the lubricating oil adhered to the cylinder inner peripheral face is diluted by fuel adhered to that inner peripheral face from a fuel injection, and this diluted lubricating oil mixes with the rest of the lubricating oil. Therefore, the degree of progression of the fuel dilution, i.e., the rate of increase in the degree of fuel dilution, can be calculated based on the amount of fuel adhered to the cylinder inner peripheral face from a fuel injection (or more accurately, a parameter that correlates with that amount of fuel).
Therefore, it is possible to accurately estimate the degree of fuel dilution together with the increase in the degree of fuel dilution by sequentially updating the value of the current degree of fuel dilution based on the calculated rate of increase and learning the updated value of the degree of fuel dilution as the value of the new degree of fuel dilution.
Also, it is difficult to directly detect the amount of fuel adhered to the cylinder inner peripheral face, but it can easily be obtained based on a parameter that correlates with the amount of this adhered fuel, such as the fuel injection quantity, the fuel injection timing, or the engine temperature, or a combination of two or more these parameters. The correlation between the amount of fuel adhered to the cylinder inner peripheral face and these parameters is as follows. The amount of fuel adhered to the cylinder inner peripheral face tends to increase (i) as the fuel injection quantity increases, (ii) as the fuel injection timing is set closer to when the piston reaches bottom dead center, and (iii) as the engine temperature decreases. Therefore, each of these tendencies are taken into consideration when obtaining the amount of fuel adhered to the cylinder inner peripheral face.
Further, the dilution degree estimating portion may estimate the degree of fuel dilution by further estimating an amount of fuel evaporated from the overall lubricating oil based on the temperature of the lubricating oil or a parameter that correlates with that temperature, calculating a rate of decrease of the degree of fuel dilution based on the estimated fuel evaporation amount, sequentially updating the degree of fuel dilution based on the calculated rate of decrease and calculated rate of increase, and learning the updated degree of fuel dilution.
The degree of fuel dilution of the overall lubricating oil is gradually reduced as the temperature of the lubricating oil increases from engine combustion heat and the like and the fuel contained within the lubricating oil evaporates. Therefore, the degree by which the fuel dilution is reduced, i.e., the rate of decrease in the degree of fuel dilution, can be calculated based on the temperature of the lubricating oil or a parameter that correlates with that temperature.
Accordingly, the degree of fuel dilution, together with both the increase and decrease in that degree of fuel dilution, can be estimated with even greater accuracy by sequentially updating the value of the current degree of fuel dilution based on not only the rate of increase, but also the rate of decrease, of the degree of fuel dilution, and learning this updated value of the degree of fuel dilution as the value of the new degree of fuel dilution.
The temperature of the lubricating oil may also be detected directly using an oil sensor or the like, or obtained based on a parameter that correlates with the engine coolant temperature or lubricating oil temperature or the like. In addition, the initial value of this lubricating oil temperature may be estimated based on the engine temperature (e.g., engine coolant temperature) at engine startup, and the amount of increase in the engine temperature may be estimated based on the total amount of combustion heat after engine startup (i.e., it may be obtained by the intake air quantity sum value or the fuel injection quantity sum value, for example). The current lubricating oil temperature may then be obtained based on the initial value and the amount of increase.